Ink jet printing has become a technology of choice for short-run printing. A recent survey on progress and trends in ink jet printing technology is given by Hue P. Le in Journal of Imaging Science and Technology Vol. 42 (1), January/February 1998, which is herein incorporated by reference.
In ink jet printing tiny drops of ink fluid are projected directly onto an ink receptor surface without physical contact between the printing device and the receptor. The printing device stores the printing data electronically and includes a mechanism for ejecting the drops image-wise. Printing is accomplished by moving the print head across the paper or vice versa.
The jetting of the ink droplets can be performed in several different ways. In a first type of process a continuous droplet stream is created by applying a pressure wave pattern. This process is known as continuous ink jet printing. In a first embodiment the droplet stream is divided into droplets which are electrostatically charged, deflected and collected, and into droplets that remain uncharged are undeflected and form the image. Alternatively, the charged deflected stream forms the image and the uncharged undeflected jet is collected. In this variant of continuous ink jet printing several jets are deflected to a different degree and thus record the image (multideflection system).
According to a second process the ink droplets can be created “on demand” (“DOD” or “drop on demand” method) whereby the printing device ejects the droplets only when they are used in imaging on a receiver thereby avoiding the complexity of drop charging, deflection hardware, and ink collection. In drop-on-demand printing the ink droplet can be formed by means of a pressure wave created by a mechanical motion of a piezoelectric transducer (so-called “piezo method”), or by means of discrete thermal pulses (so-called “bubble jet” method, or “thermal jet” method).
Ink compositions for ink jet typically include the following ingredients: dyes or pigments, water and/or organic solvents, humectants such as glycols, detergents, thickeners, polymeric binders and preservatives. Ink compositions can be roughly divided into:                water-based inks, the drying mechanism involving absorption, penetration and evaporation;        oil-based inks, the drying involving absorption and penetration;        solvent-based inks, the drying primarily involving evaporation;        hot melt or phase change inks, in which the ink vehicle is liquid at the ejection temperature but solid at room temperature and in which drying is replaced by solidification;        UV-curable inks, in which drying is replaced by polymerization.        
The first two types of ink compositions require a receiving medium that is more or less absorptive, whereas solvent based inks, hot melt inks or UV-curable inks are more suitable for non-absorbent substrates.
U.S. Pat. No. 4,303,924 is an important basic patent on ink compositions for ink jet, satisfying the need for a low solvent content, and containing a UV-curable compound. It discloses a jet drop printing process utilizing a radiation curable jet printing ink, comprising: ejecting at high speed from an orifice or orifices a radiation curable ink composition comprising a mixture of (a) 5-80% of a low molecular weight multifunctional ethylenically unsaturated material which will polymerize and cure upon irradiation, (b) 0-90% of a low molecular weight monofunctional ethylenically unsaturated material for viscosity control, cured film flexibility and bond strength, (c) 0-15% of a reactive synergist to promote curing efficiency, (d) 0.2-10% of a solvent dye colorant which does not interfere with the curing efficiency, (e) 0.5-15% of an oil soluble salt to impart conductivity, (f) 0.2-20% of a photoinitiator, and (g) 0-30% of an organic polar solvent compatible with said mixture, said radiation curable ink having a viscosity of less than about 15 centipoise, a resistivity of approximately 50-5000 ohm-cm, and a surface tension of approximately 20-70 dynes/cm so that the stream of said ink composition issuing from said orifice or orifices breaks into droplets, passing said stream of droplets through a charge ring to thereby differentially charge said droplets, selectively deflecting said differentially charged droplets and directing them toward a paper substrate positioned so as to receive a portion of said differentially charged droplets, depositing at least a portion of said droplets in a pattern on said paper substrate, and passing said substrate having said pattern deposited thereon under a radiation source for a sufficient period of time to cure said radiation curable jet printing ink whereby there is formed on said substrate a pattern which is light absorptive at infrared wavelengths, smear resistant and waterproof.
EP-A 0 071 345 discloses a jet ink composition for producing visible indicia of a substrate, the ink composition being formulated from a polymerizable epoxy resin, a colorant and a solvent, characterized in that the ink composition has at 25° C. a viscosity of 1.5 to 25 mPa.s, a resistivity of less than 4000 ohm-cm, and a velocity of sound between 800 and 2,500 meters per second, and the ink composition comprising (A) 10 to 70% by weight of an epoxy resin selected from (i) diglycidyl ethers of bisphenol A, said resin being predominantly the monomer thereof, (ii) polyepoxidized phenol or cresol novolacs, (iii) diepoxide ethers or esters having two epoxy cycloalkyl groups, (iv) polyglycidyl ethers of polyhydric alcohols, and (v) combinations thereof, the said epoxy resins being liquid at room temperature or having a Durran melting point of less than 100° C., and having an epoxy equivalent weight of less than 300; (B) 1 to 12% by weight of a photoinitiator, capable of rapidly polymerizing the epoxy resins which provides a Lewis acid effective to initiate said polymerization reaction upon exposure to a source of radiation such as ultra-violet light; (C) less than 2% by weight of a colorant that does not adversely affect cure of the epoxy resins; and (D) a solvent blend containing solvents selected from aliphatic alcohols having one to five carbon atoms, alkyl ketones having two to five carbon atoms, aromatic hydrocarbons of benzene, toluene and xylene, propylene carbonate, ethylene glycol ethers having three or four carbon atoms, alkyl acetates having two to four carbon atoms, and combinations of these solvents, the solvent blend being volatile at ambient conditions.
U.S. Pat. No. 4,680,368 discloses an ultraviolet curable ink composition comprising, as main components, (A) a polyurethane poly(meth)acrylate obtained by reacting a polyisocyanate compound of the formula:
wherein R1 is a hydrogen atom or a methyl group, and n is an integer of from 1 to 20, with a hydroxyl group-containing (meth)acrylate, and having, in one molecule, at least two (meth)acryloyl groups and at least two urethane bonds, (B) a radical polymerizable low molecular weight compound, and (C) a photopolymerization initiator.
U.S. Pat. No. 4,978,969 discloses a method for printing comprising the steps of: providing printing means for delivering ink to a substrate, said printing means comprising a thermal ink jet printing apparatus; supplying said thermal ink jet printing apparatus with an ultra-violet curable ink composition comprising in combination about 12-80% by weight ultra-violet curable adhesive, about 3-10% by weight dye pigment, and about 10-40% by weight solvent; delivering said ink composition from said thermal ink jet printing apparatus to said substrate; and applying ultra-violet light to said substrate with said ink composition thereon in an amount sufficient to form a permanent image on said substrate from said ink composition.
EP-A 0 465 039 discloses an optionally UV-A light-curable ink-jet ink comprising a colourant, a polar conductive component and as a major component of the liquid phase, one or more polymerizable monomers in which the conductive component is soluble.
EP-A 0 540 203 discloses an optionally UV-A light-curable non-conductive ink comprising a colourant and as a major component of the liquid phase, one or more polymerizable monomers.
U.S. Pat. No. 5,270,368 discloses an ink composition for use in ink jet printing comprising: a) a resin composition comprising at least two acrylate resin components, a first acrylate resin component being an aromatic acrylate resin that contains at least one pendant carboxyl group and a second resin acrylate component being an acrylated epoxy monomer or dimer; b) a photoinitiator; and c) an-organic carrier.
EP-A 0 658 607 discloses an ink comprising a pigment, a water-soluble resin, a water-soluble monomer to be set by application of energy and a photopolymerization initiator in an aqueous liquid medium.
U.S. Pat. No. 5,623,001 discloses an ultraviolet radiation curable ink-jet ink composition comprising in combination: a) water, said water content being between about 20% and 75% by weight; b) a water miscible ultra-violet curable polymerizable material; c) a photoinitiator; and d) a colorant, wherein the viscosity of said ink-jet ink composition is between about 2-40 centipoise.
U.S. Pat. No. 5,641,346 discloses a ink-jet ink comprising a colorant and a liquid component comprising water and at least one compound selected from the group consisting of epoxies and vinyl ethers.
WO 97/31071 discloses a radiation-curable ink jet composition comprising from 80% to 95% of a polyfunctional alkoxylated and/or polyfunctional polyalkoxylated acrylate monomer material; and a photoinitiator.
U.S. Pat. No. 6,110,987 discloses a photocurable composition comprising (A) 100 parts by weight of a compound with an ethylenically unsaturated bond, (B) 0.001-5 parts by weight of a cationic dye with absorptions in the visible light region of 400-740 nm, represented by general formula (1): D+·A1− (1) wherein D+ is a cationic dye with absorptions in the visible light region of 400-740 nm and A1− is an anion, (C) 0.005-10 parts by weight of a quaternary boron salt sensitizer represented by general formula (2):
wherein R1, R2, R3 and R4 each independently represent an alkyl group which may have a substituent, an aryl group which may have a substituent, an allyl group which may have a substituent, an aralkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, a silyl group which may have a substituent, a heterocyclic group or a halogen atom, and Z+ represents a quaternary ammonium cation, quaternary pyridinium cation, quaternary quinolinium cation, phosphonium cation, sulfonium cation, oxosulfonium cation, iodonium cation or metal cation, and (D) 0.01-10 parts by weight of an ultraviolet radical polymerization initiator which generates radicals upon absorption of light of wavelength 200-400 nm, wherein the ultraviolet radical polymerization initiator is a compound represented by general formula (9):
wherein Ar represents an aryl group which may have a substituent, and X represents a phosphinoyl group with a substituent. U.S. Pat. No. 6,110,987 further discloses among other monomers which may be used in the photocurable composition: (meth)acrylic polyfunctional polyorganosilsesquioxanes.
EP-A 1 302 499 discloses an active energy beam-curable composition comprising: a photo-cationic polymerizable substance; a photo-cationic polymerization initiator; and an oxetane compound.
EP-A 1 302 499 specifically discloses oxetanyl silsesquioxane. U.S. Pat. No. 6,270,561 discloses a hot melt ink composition comprising in combination: (a) a polyhedral silsesquioxane compound present in a proportion of about 0.1 to 30 wt % based on the total weight of the hot melt ink composition; (b) an ink colorant; (c) a resin; (d) a tackifier; (e) a viscosity modifier.
U.S. Pat. No. 6,461,419 discloses a cure-on-demand curable ink composition comprising a shelf stable homogeneous mixture of: at least one of: (a) a compound having 2 reactive silyl groups, and (b) a compound having at least 3 reactive silyl groups; acid generating catalyst comprising an onium salt; and pigment or pigment chip, whereby “curable” means that either reactive silyl groups hydrolyze in the presence of moisture to form compounds having silanol groups that react in the presence of an activated catalyst to form —Si—O—Si— linkages or silanol groups react in the presence of an activated catalyst to form —Si—O—Si— linkages. These moisture-curable compositions cure in the presence of moisture to form crosslinked materials, the moisture being obtained from the atmosphere, from the substrate, or it may be added to the composition.
WO 03/052014 discloses a structured hydrophilic surface with bumps and depressions, characterized in that the surface exhibits polyhedric oligomeric silicon-oxygen cluster units, which form, at least partially, the bumps. WO 03/052014 further discloses a structured hydrophilic surface characterized in that the polyhedric oligomeric silicon-oxygen cluster units are completely condensed silasesquioxanes represented by the formula R8Si8O12 with structure I
wherein the group R is the same or different and is hydrogen or a substituted or unsubstituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkinyl, cycloalkinyl, aryl or heteroaryl group.
Summarizing, a radiation curable ink composition may in general contain one or more radiation curable prepolymers, or oligomers, radiation curable monomers or reactive diluents, optionally one or more photoinitiators, colorants, and other additives. Although polymerizable monomers are in principle suited for achieving the low viscosity needed, in ink jet printing, without introducing a significant amount of water or other solvent, it is a problem to find monomers that are suitable for use both in free radically and cationically radiation curable inks.